Camellia Encryption for Kerberos 5
RFC 6803

Internet Engineering Task Force (IETF)                         G. Hudson
Request for Comments: 6803                       MIT Kerberos Consortium
Category: Informational                                    November 2012
ISSN: 2070-1721

                   Camellia Encryption for Kerberos 5

Abstract

   This document specifies two encryption types and two corresponding
   checksum types for the Kerberos cryptosystem framework defined in RFC
   3961.  The new types use the Camellia block cipher in CBC mode with
   ciphertext stealing and the CMAC algorithm for integrity protection.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6803.

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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Hudson                        Informational                     [Page 1]
RFC 6803           Camellia Encryption for Kerberos 5      November 2012

1.  Introduction

   The Camellia block cipher, described in [RFC3713], has a 128-bit
   block size and a 128-bit, 192-bit, or 256-bit key size, similar to
   AES.  This document specifies Kerberos encryption and checksum types
   for Camellia using 128-bit or 256-bit keys.  The new types conform to
   the framework specified in [RFC3961] but do not use the simplified
   profile.

   Like the simplified profile, the new types use key derivation to
   produce keys for encryption, integrity protection, and checksum
   operations.  Instead of the key derivation function described in
   [RFC3961], Section 5.1, the new types use a key derivation function
   from the family specified in [SP800-108].

   The new types use the CMAC algorithm for integrity protection and
   checksum operations.  As a consequence, they do not rely on a hash
   algorithm except when generating keys from strings.

   Like the AES encryption types [RFC3962], the new encryption types use
   CBC mode with ciphertext stealing [RFC3962] to avoid the need for
   padding.  They also use the same PBKDF2 algorithm for key generation
   from strings, with a modification to the salt string to ensure that
   different keys are generated for Camellia and AES encryption types.

2.  Protocol Key Representation

   The Camellia key space is dense, so we use random octet strings
   directly as keys.  The first bit of the Camellia bit string is the
   high bit of the first byte of the random octet string.

3.  Key Derivation

   We use a key derivation function from the family specified in
   [SP800-108], Section 5.2, "KDF in Feedback Mode".  The PRF parameter
   of the key derivation function is CMAC with Camellia-128 or
   Camellia-256 as the underlying block cipher; this PRF has an output
   size of 128 bits.  A block counter is used with a length of 4 bytes,
   represented in big-endian order.  The length of the output key in
   bits (denoted as k) is also represented as a 4-byte string in big-
   endian order.  The label input to the KDF is the usage constant
   supplied to the key derivation function, and the context is unused.
   In the following summary, | indicates concatenation.  The random-to-
   key function is the identity function, as defined in Section 6.  The
   k-truncate function is defined in [RFC3961], Section 5.1.

Hudson                        Informational                     [Page 2]
RFC 6803           Camellia Encryption for Kerberos 5      November 2012

   n = ceiling(k / 128)
   K(0) = zeros
   K(i) = CMAC(key, K(i-1) | i | constant | 0x00 | k)
   DR(key, constant) = k-truncate(K(1) | K(2) | ... | K(n))